1. Field of the Invention
The present invention relates to a fluid supply interruption free method of construction in which a construction work is carried out while allowing a fluid to flow through an existing pipeline.
2. Description of the Related Art
Up until now, buried water pipes, gas pipes, etc., have often experienced a compulsory deformation of a pipeline as a result of occurrence of earthquake or uneven settlement of the ground. The buried pipes are subjected to a tensile force and a compressive force in the pipe axial direction or to a bending force applied in the direction orthogonal to the axis of the pipe. For this reason, development has hitherto been made of various joints having a flexibility or of flexible contraction and expansion pipes.
A simple method of construction has not yet been developed that ensures an impartment of flexibility and contraction and expansion properties to the existing pipeline without fluid supply interruption.
It is therefore the object of the present invention to provide a simple fluid supply interruption free method of construction capable of imparting a flexibility and contraction and expansion properties to the existing pipeline while allowing a fluid to flow through the existing pipeline.
According to a first aspect of the present invention, to attain the above object there is provided a fluid supply interruption free method of construction in which a pit is formed in the earth so as to allow an exposure of an existing straight pipe to perform a construction work with a fluid flowing through the straight pipe, the method comprising the steps of providing a cutter having a cutting tool, and providing two sets of seal-up housings each comprising a plurality of circumferentially segmented housing parts.
The two sets of seal-up housings each hermetically enclose a part of the existing straight pipe and have a structure suited for rotations around the straight pipe in the circumferential direction of the straight pipe. Each seal-up housing has a cutting tool insertion aperture adapted for insertion of the cutting tool into the straight pipe in the radial direction of the straight pipe. The cutting tool insertion aperture has a smaller diameter than the pipe inner diameter of the straight pipe.
The method of the present invention comprises an assembly step, an infeed step, a feed step and a tool removal step.
The assembly step includes mounting said seal-up housing on the existing straight pipe to enclose a part of the straight pipe by the seal-up housing, and mounting the cutter on the cutting tool insertion aperture of each seal-up housing.
The infeed step includes causing the cutting tool to cut into the straight pipe in the radial direction of the straight pipe while turning the cutting tool to make a cutting motion for cutting the straight pipe by turns of the cutting tool.
The feed step includes rotating the seal-up housing in the circumferential direction of the straight pipe while continuing the cutting motion, the rotations causing the cutting tool to rotate in the circumferential direction of the straight pipe to make a feed motion of the cutting tool, to thereby form a cutoff groove in the straight pipe over the entire perimeter of the straight pipe.
The tool removal step includes removing the cutting tool from the seal-up housing after the formation of the cutoff groove.
The assembly step, the infeed step, the feed step and the tool removal step are executed for each of the two sets of seal-up housings.
The two sets of seal-up housings are mounted on the existing straight pipe at two axially spaced-apart locations within a single pit in the assembly step.
In the method of the present invention, the above steps are executed for each of the two sets of seal-up housings, to thereby form two axially spaced-apart cutoff grooves in the straight pipe, thus leaving a straight pipe portion between the two cutoff grooves without extraction from an existing pipe line to thereby impart a flexibility and contraction and expansion properties to the pipeline.
When a tensile force or a compressive force is applied to the pipeline finished by the present method of construction, the existing straight pipe is permitted to be displaced in the pipe axial direction of the seal-up housings. When a bending force is applied to the pipeline in the direction orthogonal to the pipe axis, the existing straight pipe is permitted to be bent relative to the seal-up housings.
In this manner, according to the present invention, contraction and expansion properties and flexibility are imparted to the pipeline.
In the present method of construction, the seal-up housings are rotated to cut off the existing straight pipe at two locations such that the straight pipe portion remains left between the two cutoff grooves without removal thereof, whereby it is possible to simply perform a construction work as compared with the case where the bite is turned for cutoff in a work tank.
The cutting tool for use in the method of construction of the present invention is preferably a milling-like (whole shape is substantially cylindrical) cutting tool having cutting edges on its tip face and outer peripheral surfaces of the tool. As used herein, the xe2x80x9cmilling-like cutting toolxe2x80x9d means a tool capable of cutting into the straight pipe and of feeding the cutting tool in the circumferential direction of the straight pipe to thereby form a groove in the straight pipe. Use of the milling-like tool enables the cutting tool insertion aperture to be diminished to achieve a reduction in size of the seal-up housings. Thus, the completed piping structure becomes compact.
The milling-like cutting tool presents a larger cutoff groove width than a milling cutter or other cutting tool. Thus, a larger tolerance is ensured for the compressive deformation of the pipeline.
The existing steel pipe jointed by welding has no flexible joint, so that application to such a steel line (pipeline) renders the present method of construction effective.
In case of cutting an existing straight pipe having a mortar lining on the inner surface of the pipe by the present method of construction, it is preferable to use a cutting tool provided with a multiplicity of chips made of a hard metal or a cutting tool having cutting edges in the form of diamond particles.
In case of cutting the steel pipe, it is preferred to use a cutting tool having cutting edges made of a high speed steel.
In the present invention, xe2x80x9cseal-upxe2x80x9d does not mean a complete seal-up but means that a watertightness is kept to such a degree as to allow a construction work without interruption of the fluid supply. Accordingly, the xe2x80x9cseal-up housingxe2x80x9d refers to a housing having a pressure resistance capable of withstanding the pressure of a fluid flowing through the interior of the existing straight pipe and having water stop properties to a certain extent. The xe2x80x9cseal-up housingxe2x80x9d may be separated into a plurality of housing parts in the pipe axial direction (e.g., see Japan Patent Laid-open Pub. Nos. Hei11-287385 and Hei11-304073), in such an instance, the entirety of the seal-up housing need not necessarily be rotated but instead a part of the seal-up housing may undergo rotations. Although in the preassembled state of the xe2x80x9cseal-up housingxe2x80x9d to the existing straight pipe, the xe2x80x9cseal-up housingxe2x80x9d is made up of a plurality of circumferentially separated housing parts, the housing parts may be integrated by welding into a circumferentially endless body after the assembly.
xe2x80x9cHermetically enclosingxe2x80x9d means that the seal-up is made to such a degree as not to impede the cutting or other works. For example, the seal-up housing may be provided with a drainage hole so that the drainage hole is opened during the cutting work to drain cutting chips together with water through the drainage hole.
In the present invention, xe2x80x9ccuttingxe2x80x9d means partly removing the pipe wall by turning the cutting edges. The xe2x80x9ccutting motionxe2x80x9d refers to turning of the cutting edges, whereas the xe2x80x9cfeed motionxe2x80x9d refers to a displacement of the cutting tool to positions where the cutting tool can sequentially cut out a fresh portion of the pipe wall.
In the present invention, the two seal-up housings may be attached to a single or two straight pipes to make sequential or simultaneous cutoff operations. In the present invention, a single seal-up housing may be attached to the existing straight pipe and mounted with the cutter to make a first cutoff, after which another seal-up housing may be attached to the straight pipe and mounted with the cutter to make a second cutoff. In the present invention, the infeed step and the feed step may simultaneously be carried out as long as the cutoff of the existing straight pipe is achieved.
Furthermore, in the present invention, the seal-up housing may previously be mounted with the cutter after which the seal-up housing may be attached to the straight pipe.
In the present invention, the cutting tool insertion aperture is typically blocked by a plug or a plate flange, but instead the operation valve may intactly be left or the insertion aperture may be fitted with an air valve, etc.